1. Field of the Invention
This invention relates to a machine for and method of making tubular conduit of indefinite length and more particularly to a so-called live surface mandrel employed with such machine and method.
2. Prior Art Statement
Machines and methods for making tubular conduit of indefinite length and having a substantially smooth inside surface have been proposed previously and often employ mandrels having a so-called live surface. For example, see U.S. Pat. Nos. 3,548,724 and 3,271,064 which employ so-called endless belts movable about a central part of a mandrel to provide the so-called live surface for such mandrel. However, a mandrel of this type which employs an endless belt to define a live surface therefor is generally expensive to construct and operate; and, it is difficult to produce a conduit of comparatively small inside diameter on a mandrel of this type.
So-called live surface mandrels have also been proposed which use a series of internal rollers to define such live surface; however, mandrels of this type are categorically considered incapable of producing conduits each having a smooth inside surface and of minimum diameter and thus prior art of mandrels of this type are not considered pertinent.